1. Field of the Invention
The present invention relates to a transport network such as SONET (Synchronous Optical NETwork) ring in which STM (synchronous transport module) traffic and high-speed LAN (local area network) traffic, such as Gigabit Ethernet, are transported in a high capacity STM path.
2. Description of the Related Art
With the proliferation of low-cost, high-speed local area networks (Gigabit Ethernet), the recent tendency of transport technology is toward using the ITU-approved standards for Generic Framing Procedure (GFP) and Virtual Concatenation (VC) for creating Ethernet services within existing high-speed TDM (time division multiplex) backbone networks as represented by the SONET ring. GFP is a framing technique that allows multiple packets of layer-2 protocols to be placed in a frame of common data structure. The GFP framing technique eliminates the flag pattern issue associated with the prior art POS (PPP over SONET) framing technique and allows efficient accommodation of many different packet services by taking advantage of statistical multiplexing capability. On the other hand, virtual concatenation significantly improves the efficiency of data transport by grouping the synchronous payload envelopes of SONET frames in a nonconsecutive manner to create virtual concatenated groups of specific size. This virtual concatenation method allows finer granularity for provisioning of bandwidth services and is an extension of an existing concatenation method (i.e., contiguous concatenation) in which groups are presented in a consecutive manner with coarse granularity. Virtual concatenation allows efficient transport of Gigabit Ethernet. In the prior art, Gigabit Ethernet is transported over SONET networks using the nearest contiguous concatenation group size available, wasting a substantial amount of communication bandwidth. For example, a VC-4 (150 Mbps) channel must be used to transport a 100-Megabit Ethernet wasting approximately 33 percent of the transport bandwidth. Virtual concatenation of two VC-3 (50 Mbps) channels can transport a 100-Megabit Ethernet channel, utilizing 100 percent of the available bandwidth.
However, since the prior art packet network has no robust monitoring system that meets the OAM (operations, administration and maintenance) requirements of a large scale transport network, transport providers are likely to experience difficulty in determining the point of responsibility when a failure occurs in the network.
Although the native SONET network is provided with a number of monitoring systems, they are specifically designed to meet the needs of its different layers (Path, Section and Line) and their coverage does not extend to the edge point of the network where it is connected to a local area network.
If the prior art monitoring system of STM path layer is used in an STM-LAN transport system, a failure on a single packet path layer would be taken as a failure of a bundle of packet path layers and more than one alarm signal is generated, producing a number of unnecessary warning signals. To avoid this problem, one-to-one provisioning must be made so that packet paths are respectively established in STM paths. However, such an arrangement would impose serious limitations on network OAM functions and the inherent advantages of statistical multiplexing capability of packets and the flexible bandwidth allocation of virtual concatenation cannot be fully exploited.
A number of path monitor systems are known. In the path monitor system disclosed in Japanese Patent Publication 2001-53756, an information signal from an input interface port is switched through an n×n switch to an output interface port according to path setup information supplied from a scheduler. The established path is monitored by checking parity bits of the information signal. In order to monitor paths which are not established due to invalid path setup information, a counter is provided at each output interface port for incrementing its count value when the path setup data is determined to be invalid. The incremented count value is transmitted in a packet as path setup data, which is also used at a receive site as a path supervisory signal.
Japanese Patent Publication 1995-46238 discloses a monitoring system for a packet routing network. In this system, path inspection packets are inserted into the routing network and routed through different paths. When each packet passes through a strategic point of the network, it is given information identifying the passing point. The inspection packets are then removed from the network and their passing point information is checked against known scheduling information. If no coincidence is detected, it is determined that there is an abnormal condition in the routing network and a warning signal is generated.
A paper entitled “GFP Breakout group report and GFP Revision 1”, Enrique Hernandez-Valencia, prepared by Lucent Technologies Inc. as a Contribution to T1 Standards Project (Digital Optical Hierarchy) describes an OAM aspect of the GFP control frame format. However, the transport mechanism of the GFP frame is still at open issue.